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Carbon dioxide (CO2) separation plays a vital role in environmental protection and resource reuse. A potential approach to achieving satisfactory CO2separation is combining the benefits of ionic liquids (ILs) and membranes. In this work, the IL-LDH nanosheets were obtained by functionalized IL modifying layered double hydroxides (LDH) and used to construct the Pebax/IL-LDH mixed matrix membranes (MMMs). The X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) spectra analysis displayed that the IL was successfully grafted to the LDH nanosheets. The characterizations of MMMs showed that the introduction of IL-LDH reduces the crystallinity of the Pebax membrane, and there are hydrogen bond interactions between fillers and Pebax. The IL modification strengthens the membranes with better CO2affinity and improves the interfacial compatibility between Pebax and LDH. Meanwhile, the CO2-philic nanochannels formed by the slits of IL-LDH nanosheets facilitate CO2transport in MMMs. Such inherent properties of the IL and LDH conjunctly contribute to the improvement of the CO2separation performance of membranes. The optimum Pebax/IL(20)-LDH MMM has a high CO2permeability of ∼388 barrer at 30 °C, which is approximately 2.9 times that of pure Pebax, and the CO2/CH4selectivity does not change significantly. Besides, the Pebax/IL(20)-LDH MMM exhibited a notable increase in CO2permeability as the working temperature increased, ultimately attaining ∼576 barrer at 50 °C.

In this work, a series of novel CO2absorption solvents were prepared using solid tetramethylammonium cation-based ionic liquids and water. Herein, for the first time, tetramethylammonium cations-based ionic liquids ([N1111][AHA], namely [N1111][Py], [N1111][Im], and [N1111][1,2,4-Tz]) with aprotic heterocyclic anion were synthesized. The viscosity of these absorbents ([N1111][AHA]/H2O), composed of different contents of [N1111][AHA] and H2O, was measured, indicating that their viscosity was below 50 mPa·s at 313.15 K. Moreover, the anion structure significantly affected the CO2absorption performance. The CO2absorption capacity increased in the order of [N1111][Py]/H2O > [N1111][Im] /H2O > [N1111][1,2,4-Tz]/H2O, with only [N1111][1,2,4-Tz]/H2O presenting excellent reversibility (5 cycles). The optimal solvent composition was 80 wt % [N1111][1,2,4-Tz] and 20 wt % H2O, yielding a CO2absorption capacity of 0.268 g CO2/g absorbent and the ideal selectivity for CO2/N2and CO2/O2was 1217.8 and 911.1, respectively, at 313.15 K and 100 kPa CO2. The study of the CO2absorption mechanism was investigated using 13C NMR, in situ FTIR, and DFT calculations, showing that water can cooperate with ILs to absorb CO2. Carbamate and carbonate were formed during CO2absorption, which is beneficial for CO2capture. These novel [N1111][AHA] solutions are potential absorbents for CO2separation in flue gas.

A novel dual amino-functionalized ionic liquid, 1, 3-di (2′-aminoethyl)-2-methylimidazolium bromide (DAIL), was synthesized and investigated as a potential absorbent for CO2capture. CO2absorption behavior on pressure, temperature and concentrations of DAIL in aqueous solution were studied, and the absorption mechanism was investigated by spectroscopic methods and DFT calculations. The CO2capture capacity of 18.5 wt % and good thermal stability (Td= 521.6 K) make DAIL a good candidate for industrial applications for CO2capture.

In this paper, the two-phase flow and mass transfer process of CO2and [C2OHmim][Lys]/MDEA mixed aqueous solution in a T-shaped microchannel were investigated systematically. By using a high-speed camera connected to a computer, the two-phase flow patterns were recorded online, including the Taylor flow and a small amount of Taylor-bubbly flow. And the effects of ionic liquid concentration and two-phase flow ratio (QG/QL) on bubble length, specific surface area, gas holdup, and mass transfer coefficient were studied experimentally. The results indicate that the blended solution of [C2OHmim][Lys]/MDEA could significantly enhance two-phase mass transfer compared to single N-methyldiethanolamine aqueous solution. The reaction mechanism between CO2and ionic liquid/amine mixed aqueous solution was also analyzed. On the basis of experimental data, some new correlations for predicting the bubble initial length and the volumetric mass transfer coefficient were proposed, which matched well with the experimental data. This work is helpful to provide new ideas for the design of CO2absorbents and further improve the data of gas–liquid mass transfer in microchannels.

Aluminum, as an associated metal with rare-earth resources, is a common impurity in rare-earth separation products. In the traditional P507-kerosene-HCl system, tremendous aluminum impurity (8875 mg/L herein) is often enriched in GdCl3solutions because of the similar extraction sequence during rare-earth separation. In this work, a new amine-group-functionalized ionic liquid (IL) was developed to remove trace aluminum impurity from high-purity GdCl3solutions, overcoming the drawbacks of strong hydrophilicity and complicated compositions of the organic phase, as well as other impurities introduced and tremendous saline wastewater produced inevitably. Methyltrioctylammonium hydroxide (N1888OH), instead of the water soluble ammonium hydroxide (NH4OH), was used to dissociate the dimer of sec-octylphenoxy acetic acid (CA12) and synthesize cation- and anion-bifunctionalized IL [N1888][CA12]. The separation factor of Al/Gd was as high as 36. The influences of pH, salting-out agent, extraction time, temperature, and stripping efficiency on the extraction efficiency were evaluated. The result showed that high-purity GdCl3solution was obtained with low aluminum impurity of 10 ppm after five-stage countercurrent extraction. Due to the weak interaction between the metal and IL, very dilute HCl solution (0.07 mol/L) and NaOH solution (0.07 mol/L) were in favor of metal stripping and IL regeneration.